Method for making titanium nitride from phosphates



METHOD FOR MAKING TlTANIUM NITRIDE FROM PHOSPHATES Application September 23, 1953 Serial No. 381,960

Claims. (Cl. 23-191) No Drawing.

The present invention relates in general to refractory metal compounds and more particularly to titanium compounds of nitrogen and to an improved method for making the same.

Heretofore refractory metal compounds of carbon, zirconium and the like, sometimes referred to hereinafter as metalloids, have been prepared with a modicum of success by heating dry mixtures of a refractory metal oxide, such as for example calcined titanium dioxide or zirconium oxide and carbon to form the refractory metal carbide. However, prior methods have had to contend with the problem of obtaining intimate and permanent contact between the inherently coarse metal oxide particles, and the carbon particles which, due to their fineness, tend to separate out from the mixture during reaction. In attempting to overcome this difficulty, prior technicians have resorted to pelletizing the mixtures and then heating the pellets at temperatures from 2000 C. to 2500 C. The resulting product is a hard sintered mass of material which must be subsequently broken up into smaller particles and ground. However, such products can be ground mechanically to form a finely divided powder only with great difficulty due to the abrasiveness and hardness of the compositions. Hence, even the ground material is relatively coarse, the smallest particle size being about 80 microns. Moreover, the purity and toughness of this product is often impaired by a high percentage of graphite which forms when excess carbon is dissolved in titanium carbide; or by partial dissociation of the carbide at temperatures above 2000. Although these relatively coarse products have been used in the field of powder metallurgy, the impurity and coarse granular nature of the material has impaired its usefulness. There is, therefore, no direct and commercially practicable method for producing finely divided relatively pure refractory metal compounds of nitrogen, without recourse to grinding and milling operations.

An object, therefore, of the present invention is to provide an improved method for making a refractory metal economical, which may low temperatures and which divided be carried out at relatively is productive directly of a relatively pure finely product.

A further object of the invention is to provide a superior method for forming a mixture of carbon, a refractory metal and nitrogen wherein the carbon particles are maintained in intimate contact with the refractory metal.

A still further object of the invention is to provide substantially pure finely divided particles of titanium nitride.

These and other objects will become apparent from the following more complete description of the instant invention.

The term finely divided as used herein with reference to the size of the titanium nitride particles formed directly by the process of this invention shall be understood to mean that the efiective sizes of the particles may vary from 1 to 50 microns.

in its broadest aspects, the present invention relates to 0 fine powder to 2,2234% Patented Feb. 4, 1958 a new and improved titanium nitride composition; and to an improved method for making said compound which comprises forming an intimate mixture of a titanium phosphate and carbon, and then heating the mixture in an atmosphere of nitrogen at a temperature of from 1100 C. and higher until the reaction is completed, generally at about l600 C. to produce a finely divided titanium nitride.

In carrying out the invention it was discovered that the successful production of substantially pure finely divided titanium nitride is dependent, in large measure, upon achieving an intimate mixture of the carbon and titanium components. As pointed out above, due to the coarseness of calcined oxides of titanium, as compared to the particle size of lamp black, it is extremely difficult to form and maintain an intimate mixture of calcined titanium dioxide and finely divided carbon. However, the instant invention embraces the discovery that the problem of forming intimate mixtures of the titanium values and carbon can be effectively solved by providing the titanium values in the form of a titanium phosphate prepared by reacting titania hydrate with phosphoric acid.

The titania hydrate used in carrying out the process of this invention may be titania metahydrate or titania orthohydrate and is preferably an untreated hydrate which occurs as an intermediate product in the production of titanium dioxide pigment and which is generally referred to in the art as pulp. This untreated titania hydrate, or pulp, comprises particles, i. e. crystalloids or groups of crystalloids, the efiective sizes of which may vary from 0.05 to 0.2 micron. Since the untreated pulp is usually formed by hydrolyzing an acid solution of titaniferous ore, the untreated pulp will contain or be combined with about 10% sulfuric, or hydrochloric acid, depending on the kind of acid solution used, and although the presence of the acid in the hydrate is not known to have a deleterious effect on the process or product of the invention, it is within the purview of the invention to remove the acid fraction from the hydrate by any of the techniques well known to the art of pigment manufacture.

In achieving the objects of this invention it was discovered that when finely divided carbon is mixed with a titanium phosphate, the particles of carbon are not only thoroughly and completely dispersed throughout the mixture but that the fine particle sizes greatly enhance the reactivity thereof such that when dried, the mixture may be calcined at relatively low temperatures in an atmosphere of nitrogen to produce a substantially pure finely divided titanium nitride.

With respect to the carbon used in the mixture of materials, a finely divided carbon, such as lamp black or oil burner soot, is suitable, the unit particles of which have an effective size of from about 0.01 to 0.05 micron. It is also within the purview of the invention to use a hydrophilic carbon, that is to say a carbon which has been treated with a suitable wetting agent, as for example one of the polyethylene glycol type, to insure dispersion of the carbon particles in an aqueous medium; or a wetting agent may be added to the admixed titanium phosphate and carbon.

in carrying out the process of this invention for the preparation of titanium carbide, the carbon may be admixed with the titanium phosphate in either of two ways. One way is to form the titanium phosphate first by mixing an aqueous slurry of titania hydrate with phosphoric acid in substantially stoichiometric amounts, partially drying the mixture and then heating the dried mixture to form the pyrophosphate having the formula T iPgOq- The pyrophosphate is recovered in the form of a dry which is added the stoichiometric amount of dry carbon. After thoroughly mixing the dry pow- 3 4 ders in a mortar or other suitable means, the mixture While this invention has been described and illu rated is transferred directly to calcining means, such as for y the examples SIIOWII, it is not intended to be Strictly x l an i d ti furnace or a rotating kiln capable limited thereto, and other variations and modifications of maintaining the temperatures required for calcining, y be p y Within the Scope of the following thepowdered material. The material is calcined at tem- 5 Claims. peratures of from about 1100 C. to as high as about We claim: 1600 C. for from about 2 to 4 hours in an atmosphere 1. Method for. the'production of titanium nitride which of nitrogen comprises forming an intimate and at least stoichiometric The reaction between the titanium pyrophosphate and mixture of titanium pyrophosphate and carbon and heatcarbon during calcination in the presence of nitrogen may ing said mixture in anatmosphere of nitrogen at a tembe represented by the following equation: perature of from about 1100 C. to about 1600 C. to calcine said-mixture and produce titanium nitride having 2T1P207+14C+N3+2T1N+4P+14C0 a particle size in the range of from 1 to 50 microns wherein 2 mols of titanium dioxide added in the form of 2, Method f r the roduction of titanium nitride which titanium PY P P react With 14 111015 of 0- 15 comprises admixing an aqueous titania hydrate slurry and l molof nitrogen t0 form 2 111018 Of titanium llltl'ld, with phosphonc ac d and lamp black agitating the n- 4 111015 of Phosphorus and I4 mols 0f CaI'bOH ITIOHOXldegredients to form an intimate and at least stoichiometnc e final Pmdllct 1s a Olden Yellow mfitalllc Powder mixture of said hydrate phosphoric acid and lamp black having substantially no free carbon, the Percentage of and then heating said-mixture in an atmosphere of nitrotitanium present being from 78% to. 80% and the pergm t a t t fr 1100 C. t 1600 C. to calcentage of nitrogen present being fr m 1 to 2 cine said mixture and produce titanium nitride having a which compares favorably With the theoretical composiparticlesize in the range of from 1 to 50 microns, tion of pure titanium nitride. The Size of h i n 3; Method for the. production of titanium nitride which nitride particles formed directly by calcination of the comprises: admixing anaqueous titania hydrate slurry pyrophosphate and carbon in an atmosphere of nitrogen, with phosphoric acid and heating the mixture to form t at is to say without subsequent grinding, varies from tit iu pyrophosphate, admixm at least a stoichioto 15 microns and y be smaller if somewhat higher metric amount of finely divided carbon with sald tltanlurn calcining temperatures are used. pyrophosphate, and then heating said mixture in an at- As an alternative method of m1x1ng the carbon and mosphere of n trogen to a temperature from 1100 C i ni m values, a p rmine m n f r n, pr fto 1600 C. to calcine. said mixture and produce titanium erably a Y P C Carben Which is miscible in an q nitride having a particle size in the range of from 1 to 50 ous medium, is added to a mixture of phosphoric acid mi ron and aqueous titania hydrate Slurry and the ingredients 4. Method for the production of a titanium nitride thoroughly mixed by agitation after which the mixture which comprises: mixing an aqueous substantially acidmay be partially dried by heating at relatively low temfree titaniahydrate. slurry with phosphoric acid and a Peratufes, as for 131 from 150 to The hydrophilic carbon, agitating said ingredients to form dry or partially dried mixture 15 then broken up to prean intimate and at least stoiclnometric admixture of said vi e a fine powder whic is calcined 1n the manner herehydrate, hos hor a id and carbon, partially drying inabove described to form titanium nitrid said admixture and then heating the partially dried mix- To further illustrate the invention, the following extime t a temperature of from 1100 C. to 1600 C. in ample is given: an atmosphere of nitrogen to calcine said mixture and Example I produce titanium nitride having a particle size in the To. lOlparts by weight of titanium pyrophosphate prerange of from 1 to 50 mlcrons: paredfrom an admixture of titania hydrate and phos- Method for F, of a mmde phon-c acidlwere added 4 parts by Weight of Carbon in which compnses mixing an aqueous substantially acidthe form of: a carbon black powder. The mixture was free mama hydrate Slurry Wlth Phosphor acld carbon worked for a sufiicient len th of time to insure an intia Wettmg agent agltatmg 331d Ingredients to form mate mixture f he py flphosphate and carbon particles n ntimate and at least stotchiometric admixture of said whereupon the mixture was introduced into a resistance hyfh'ate phcsphonc acld Carbon i i drylpg furnace and calcined at a temperature of about 150i) C Bald admixture andthen heating theopa'mauy druid for two hours m an atmosphem of nitrogen ture to atemperature of from 1109 C. to 1e00 C. in The resulting product comprised a finely divided tig l of'nitrpgen calcme 5 i i and tam-um nitride powder the effective Size of the unitpap produce titanium nitride having a particle size in the ticles being from- 1 to 5 microns. An analysis of the range of from 1 to 50 microns l 9" product showed about 7 ,o tit nium and 21% nitrogen Referencesvclted m the file of fins patent vention, metalloids ofirefractory metals, and in. particular UNITED STATES PATENTS titanium nitride, maybe produced in an efiicientandeco- 57 42 Bosch May 10 1910 nemical manner and from relatively inexpensive source o 027 312 Bosch et 1 May 21, 1912 materials. Moreover, the temperaturesemployed are 1 59 939 P ak fi 9 5 relatively low, thereby precluding sintering and, the formation of relatively large size agglomerates, the. calcining FOREIGN PATENTS temperature for titanium nitride being from about; 1100 522,487 Belgium Dec. 16, 1953 C. to about 1500 C. Further, the finely divided product 23,8 GTeafBIitBifl 1902 of this invention has an efiective particle size ranging 277,715 Great Britain Dec. 20, 1928 from 1 to St) microns but mostly of from 1 to. 15 microns; OTHER REFERENCES and-are quite free of free carbon, occluded graphite or other foreign materials. This highly superior titanium Menor CQmPIeEeDSWQ Treatise nitride is thus ideally suited for use in powder metallurgy; game and Theoretical Chem-i Pages as abrasives, and in the production of cutting tool alloys Longmans, Green and 

1. METHOD FOR THE PRODUCTION OF TITANIUM NITRIDE WHICH COMPRISES FORMING AN INTIMATE AND AT LEAST STOICHIOMETRIC MIXTURE OF TITANIUM PYROPHOSPHATE AND CARBON AND HEATING SAID MIXTURE IN AN ATMOSPHERE OF NITROGEN AT A TEMPERATURE OF FROM ABOUT 1100*C. TO ABOUT 1600*C. TO CALCINE SAID MIXTURE AND PRODUCE TITANIUM NITRIDE HAVING A PARTICLE SIZE IN THE RANGE OF FROM 1 TO 50 MICRONS. 